AFMAsylum Research
Variable Field Module Allows Study of Samples
Under Either In-Plane or Out-of-Plane Magnetic Fields
Introduction
The Variable Field Module (VFM4) is an accessory for Asylum
Research MFP-3D atomic force microscopes (AFMs) that enables
researchers to apply an adjustable magnetic field either in-planewith the sample or out-of-plane while simultaneously making
AFM measurements (Figure 1). Though most often used inconjunction with magnetic force microscopy (MFM), the VFM4
is also used with techniques like conductive AFM (CAFM) andon diverse samples including piezoelectric and ferroelectricmaterials. No other commercial solution offers the same
capabilities, versatility, and ease of use for magnetics research.

Figure 1: VFM4 Variable Field Module
The VFM4 is a small stage that easily mounts to the MFP-3D scanner.
The photo shows it in the in-plane field configuration.

Applying In-Plane Magnetic Fields
Figure 2 shows a diagram of the VFM4 configured for in-planemagnetic fields. For highest field strength (up to ±8000 G) andbest field uniformity, small, thin samples are used and placed
directly between the two removable pole pieces.
Figure 3 demonstrates the effect of an increasing magnetic
field on bits written to a piece of PMR (perpendicular magneticrecording) hard disk. The bits are progressively degaussed as thein-plane magnetic field is increased from zero to >7000 G.
Figure 4 presents MFM phase images of a Terfenol-D disk during
and after application of in-plane fields applied perpendicular tothe direction of magnetization in the film.
Removablepole piece

SampleSensor
Soft iron(gray parts)

Removablepole piece

Figure 3: Degaussing bits on PMR hard drive
Three MFM images showing a piece of PMR hard disk that is eventuallydegaussed when the in-plane magnetic field reaches 7000 G.

Rotating
permanentmagnet

H=0 G; θ=0˚

Figure 4: Effect of in-plane field on Terfenol-D film
MFM phase images of the Terfenol-D disk, 10 μm scans. (left) Imaged
while under a -2000 G field, and (right) after field removal. Image
courtesy of S. Xie, Xiangtan Univ. and J. Li, Univ. Washington.
H=8000 G; θ=90˚

Figure 2: Schematic of in-plane field configuration
The strength and sign of the magnetic field applied to the sample
depends on the rotation angle (θ) of the rare earth magnet. At 0° or
180°, the magnetic flux is shunted away from the sample by the soft ironarmature and pole pieces. As the magnet rotates, more and more flux is
coupled instead through the sample. At 90,° the field is maximized.

Applying Out-of-Plane Magnetic Fields

0G70 G

150 G

Figure 5 shows how the removable pole pieces of the VFM4
allow it to be reconfigured for out-of-plane magnetic fields.
The flux lines are sketched in an idealized way here, but inreality, the longer, less direct path necessitated by placementof the AFM head above the sample reduces the maximum
achievable field to about ±1200 G.
Figure 6 shows one example from a separate Application Note,“Magnetic Force Microscopy Under Applied Perpendicular Fields
with Asylum Research AFMs,” which can be found on ourwebsite at: http://AFM.oxinst.com/OOP-MFM

Figure 6: Magnetic skyrmions in Co-based thin film pads
Imaged with MFM under out-of-plane magnetic fields. Each pad is~900 nm in diameter. Images courtesy of K. Bouzehouane, Unité Mixtede Physique CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, France.

Features and Benefits
Removablepole piece

SampleSensorposition

Removablepole piece• Easily configurable for applying both in-plane and•

Rotating
permanentmagnet

Soft iron(gray parts)

H=0 G; θ=0˚•••

out-of-plane magnetic fields
Unique design uses a permanent magnet, eliminating
the large thermal drift caused by field generators thatuse electromagnets.
Field strength adjustment is motorized and can becontrolled using linear ramps.
Integrated Hall sensor measures the in-plane fieldstrength, while an external Gaussmeter is provided formeasuring the out-of-plane field strength.
Optional kit allows application of a high-voltage tip
bias (adjustable, ±150 V for MFP-3D Infinity or±220 V for MFP-3D Origin+).

VFM4 Specifications• Field directions: Includes both in-plane and out-of•••plane capabilities, easily reconfigured by the user
Maximum field: ±8000 G in-plane
Maximum field ±1200 G out-of-plane (±1500 G typ.)Environmental controls: Ambient only (no heating,cooling, or closed cell available concurrent with VFM)

H=1200 G; θ=90˚Figure 5: Schematic of out-of-plane field configuration
The out-of-plane configuration works with the same principles as thein‑plane configuration, except that the sample is placed on one pole ofthe iron armature, well-separated from the other pole, such that the flux
lines run through the plane of the sample. Both configurations place thesensor at a position symmetric in the field relative to the sample to avoid
a positional offset error and to achieve better accuracy.

Think the VFM4 might be helpful
to your research? Let’s talk!
Email: AFM.info@oxinst.com, or
Call: +1-805-696-6466

The foregoing brochure is copyrighted by Oxford Instruments Asylum Research, Inc. Oxford Instruments Asylum Research, Inc.
does not intend the brochure or any part thereof to form part of any order or contract or regarded as a representation relating
to the products or service concerned, but it may, with acknowledgement to Oxford Instruments Asylum Research, Inc., be used,applied or reproduced for any purpose. Oxford Instruments Asylum Research, Inc. reserves the right to alter, without notice thespecification, design or conditions of supply of any product or service. Datasheet #39 – 4/2018.

6310 Hollister Avenue
Santa Barbara, CA 93117
Voice+1 (805) 696-6466
Toll free +1 (888) 472-2795
Fax+1 (805) 696-6444

Web: http://AFM.oxinst.com
Email: AFM.info@oxinst.com